State of Extraction of Oil and Gas from Coal
There is a great deal of attention to the extraction of oil and gas from oil shale and tar sands using conventional heating and electromagnetic energy or a combination of both. However, there is hardly any attention to the possibility that oil and gas can be produced from most coal material from low rank to high rank coals that contain volatile material. In our discovery, it seems more profitable to extract oil and gas from a coal material than selling the coal as fuel for an electric power plant. These situations occur when the carbonaceous or coal deposit contains too much ash in very fine dissemination with the carbonaceous material as to make the coal inefficient for burning in a power plant. Another reason may be that there are toxic impurities in the coal that make the coal unsuitable as a fuel for a power plant such as high contents of chlorine, sulphur, and toxic metals such as arsenic, vanadium, mercury and lead. Another reason is the coal deposit is too deep to mine economically.
Up-grading of Coal Feed to a Power Plant
There appears no commercial operation of up-grading coal feed to a power plant to extract oil from the coal before the coal is burnt in the power plant. David Jones in his U.S. Pat. No. 5,999,888 has proposed a thermal method of extracting oil from coal by using silica balls as a heat transfer agent in the pyrolysis of the coal. The pyrolysis of coal to produce liquids by conventional heating is a well known art but the liquid produced is crude oil in the C35 (heavy oil) region and there are many other coal chemicals produced, some being toxic.
Dr. Wilhelm Achim in his patent DE 33 45 563 proposed the contact of the coal with aromatic hydrocarbons such as toluene at 400 C to 600 C in counter current in several fluid bed reactors contained in a column. Dr. Achim claims a higher recovery of oil. My research suggests that fluid beds as described by Dr. Achim will be difficult to operate because at a certain point in the pyrolysis, about 300 C to 350 C, there is a sudden high evolution of gases that will make the fluid bed unstable. In my invention, I deliberately avoided the use of dense fluidized beds to carry out the microwave pyrolysis.
The SASOL process and the SHELL process gasify the coal in a water gas reaction to produce carbon monoxide and hydrogen and these gases are combined in a Fischer Tropsch process to produce petroleum fuels such as automotive diesel. The SASOL, the SHELL and similar processes totally converting the coal to liquid petroleum are not suitable for up-grading coal feed to power plants because of the low thermal efficiency in converting the coal to petroleum and relatively small amount of gas to feed to a power plant to produce electricity.
The Ignite Process processes the coal in a reactor that operates at the critical temperature of water, about 375 C. The claim of the inventor is that as much as 2 barrels of oil are produced per tonne of brown coal but the oil produced is of low quality and is suitable for mixing with marine diesel, a low grade fuel.
The Synfuel China process treats a slurry of black coal and water with catalyst that is heated to temperatures, ranging from 245 C to 295 C, producing synfuel gas of CO and H2 that is then converted to petroleum using the Fischer Tropsch process. The slow kinetics of this process would be a deterrent to commercial application.
Franz Rotter in U.S. Pat. No. 4,308,103 (Dec. 29, 1981) pyrolyzed coal in a chamber fitted with rotating arms with the chamber heated by burning gas in an external chamber. The process produced solids, hydrocarbon gas, and hydrocarbon liquid. Rotter claimed his invention applied to carbonaceous material such as coal, rubber tyres, sawdust, and municipal waste.
Many other technologies to dry the coal, particularly for high moisture brown coal, prepare the brown coal to a lower moisture content to make the combustion more efficient, similar to the use of black steaming coal. An example is the hydrothermal drying of coal where the fine coal slurry is heated to more than 300 C at high pressure in a counter-current system to remove the water from the coal. Another is the Coldry process where the water is squeezed out of the coal in a cold process. The EXERGEN process treats a slurry of coal and water at high pressure and temperature greater than 300 C to remove the moisture from the brown coal. However, in Australia, the boilers are made to accept the brown coal with the high moisture and brown coal with moisture below 50% or 55% moisture is not acceptable to the existing boilers.
Microwave Processing of Coal to Extract Oil
There are many patents filed overseas and Australia on the use of microwaves to extract oil from coal but so far, none of these processes have been applied commercially. It is relatively easy to carry out small scale experiments using microwaves and then project these to commercial scale without demonstrating the successful use of microwaves in a commercial operation.
At the Wollongong University, New South Wales, in the early nineties, microwave processing of coal was carried out in a small pilot plant including the processing of coal from the Leigh Creek field of South Australia. It was claimed that lighter oil was produced compared to conventional heat pyrolysis of coal. The project was abandoned when further test of microwaving of the coal in a Canadian research organization did not confirm the results obtained at Wollongong University.
U.S. Pat. No. 3,449,213 E. Knapp et al (Jun. 10, 1969). Knapp proposed the preheating of the coal in a belt conveyor to 600 F (316 C) followed by the coal being radiated with microwave energy in another conveyor at 800 F in a partial vacuum. The coal chemical are recovered in an oil bath and then fractionated to recover the coal chemicals. A major scientific shortcoming of Knapp's process is that it does not address the removal of oxygen prior to pyrolysis.
U.S. Pat. No. 3,503,865 R. D. Stone et al (Mar. 31, 1970). This patent described the conditions where microwave higher than 1,000 megacycles is applied to bituminous coal at 100 C to 500 C and pressure of 15 to 10,000 psig in the presence of solvent such as tetralins, benzene and phenanthrenes and hydrogen. A very high conversion of 50% to liquids is claimed. The invention did not describe a commercial method of carrying out the process. This process does not address the removal of oxygen that would reduce the production of crude oil from the coal.
U.S. Pat. No. 4,419,214 V. Balint et al (Dec. 6, 1983). Balint describes a process of recovering oil or tar from material such as oil shale, or young coal ranks by subjecting microwaves in a pressure vessel with an expelling medium such as liquefied carbon dioxide or mixed hydrocarbon gases an “Aromatol.” For oil shale, the microwave of 0.9 to 2.5 GHz is applied for 10 to 15 minutes at a temperature of below 200 C and a pressure of 85 to 100 bars giving a yield of 65% of the organic content of the oil shale. Balint has not described a commercial method of applying his process, and Balint does not address the removal of oxygen from the coal before pyrolysis, which is aggravated by the application of pressure during pyrolysis.
US Patent Application No. 20100096295 of Carl Everleigh, Julian Forthe, and Frank G. Pringle proposes to extract oil and gas from hydrocarbon bearing solids such as oil shale, coal, car tyres, petroleum waste within the microwave frequency of 4 GHz to 18 GHz with 4 GHZ to 12 GHz as being the preferred frequency range, with the operation performed at a pressure less than 1 atmosphere or vacuum as described by Knapp in U.S. Pat. No. 3,449,213. The microwave applied is described as variable frequency microwave (VFM) as described in U.S. Pat. Nos. 5,321,222 and 5,521,360 with the aim of applying a more uniform microwave without forming hot spots. The experimental work of Everleigh et al was concentrated on tyres, oil drill cuttings, and plastics; there was no experimental work reported on the microwave processing of coal to extract oil and gas.
Coal is a very complex material and the successful commercial extraction of good quality crude oil from coal depends not only on the application of microwaves but also in the process to carry out the extraction of oil. Coal, particularly brown coal, has large amounts of oxygen in their chemical and physical structure, and the hydrocarbon molecules are generally long chains that produce less oil that is heavy oil when pyrolyzed. The use of variable frequency microwaves to achieve uniform heating as proposed by Everleigh's and Pringles's patent application will generally produce heavy crude oil which is less valuable than light crude oil. The use of VFM will heat the coal uniformly similar to conventional heat and result in the production of less crude oil that is heavy crude oil.
Canadian Patent Application 2 611 533 (2007 Nov. 27). This application seems to be a collection of thoughts for the microwave assisted extraction of oils from tar sands, plastics, rubber, bituminous coal and biomass. My reading of this patent application is that it is a recitation of the microwave processes covered by the previous US patents described above. Further, there was no specific commercial apparatus described or claimed in this patent application.
The Science of Coal Analysis
FIG. 1 shows the proximate and ultimate analysis of an Australian steaming coal and a brown coal. The major emphasis of the present invention is brown coal due to the relatively large world reserves of this coal and the inefficient burning of this coal in power plants due to the high moisture content; however, the process appears to work better with higher rank coals. The oxygen in the volatile matter in coal may be physically or chemically bound but it would be detrimental to the production of crude oil as the oxygen in close proximity to the hydrocarbons, would react to produce carbon monoxide and carbon dioxide as soon as the reaction temperature is reached which is normally below the pyrolysis temperature of 450 C to 720 C. I have considered the following methods to remove oxygen and oxygen compounds from the coal:                1. Application of hydrogen at high pressure before heating up the coal/hydrogen mixture. The use of methane was also considered. After a few test using hydrogen, I abandoned this concept because it was difficult to place the hydrogen atom next to the oxygen atom before pyrolysis temperature is reached, and because of the expense of the hydrogen and the equipment to carry out this method of oxygen removal.        2. Application of vacuum while the coal is being irradiated with microwaves of the right characteristics. This simpleprocess is my favoured process and my experiments indicated it to be successful in removing oxygen from the coal.        
The main purpose of microwaves in my invention is to break up the long chain hydrocarbon molecules that are abundant in the coal as compared to crude oil, into shorter chain molecules to produce more light crude oil that is more valuable than heavy crude oil. Instead of a variable microwave frequency, the frequency in the present invention is a single frequency to cut the long chain hydrocarbon molecules to shorter chain molecules; furthermore, the single frequency microwave is delivered to the coal charge in a pulsing mode, preferably a square wave instead of a sine wave. The effect of the pulsing would be similar to driving a nail into a piece of wood with a hammer; tapping the hammer on the nail drives the nail into the wood with less energy than driving the nail into the wood with a constant force. This microwave system is preferably fitted with an automatic tuner before the microwave is delivered to the reactor to achieve the highest possible absorption by the coal charge. In this invention, the linear microwave generated by the magnetron is preferably converted to circular polarised microwave before entering the reaction chamber to provide a more efficient action of the charge. FIG. 2 to diagrammatically describe the breaking up of long chains to shorter chain hydrocarbon molecules in the coal.
The ultimate objective of this invention is to develop simple commercial methods of economically carrying out a dry method of extracting oil from coal using electromagnetic energy.